Three ads trumpeting the high welfare standards of pork sold with the Red Tractor quality mark have been banned by the Advertising Standards Authority (ASA), which found the claims could mislead consumers into thinking pig welfare in Britain was better than it is.

"This is a victory for consumers, who deserve to be able to choose higher welfare meat without being misled," said Joyce D'Silva from campaign group Compassion in World Farming (CIWF), which made the complaint.

"Claims of high welfare are clearly a lucrative marketing tool but in this case they were overblown and misleading to the consumer.

"The 'pork not porkies' claim on the advert makes this a particularly embarrassing own-goal for Red Tractor pork.

"This is also a victory for those pig farmers in the UK who adhere to higher welfare standards like the Soil Association's organic standard or the RSPCA's Freedom Food."

Most British farms are members of the Red Tractor scheme, a label of the Assured Food Standards scheme, accounting for 40% of pork sold on UK shelves.

The Agriculture and Horticulture Development Board told ASA the three ads it commissioned were intended to compare the welfare standards of Britain and pork imported from many EU countries, where sow stalls are still in use despite an imminent EU ban and castration is still common practice.

The ASA said that this comparison was unclear and that consumers could interpret the ads as championing the general level of pig welfare in the UK.

"We considered that the claim implied that there were no concerns about the welfare of pigs in the UK, whereas some areas were unlikely to be regarded as 'high' welfare," it said in its adjudication.

CIWF has said it is particularly concerned by the scheme's guidelines on the use of slatted flooring and farrowing crates for sows.

D'Silva said: "The Red Tractor labelling scheme for pork does not guarantee high welfare and we are delighted that the ASA agrees with us that the claim was misleading."

In a statement, the RSPCA said that although some Red Tractor farms went "well above" the basic scheme requirements, others were failing to meet all the animals' needs.

But it added: "Under the Red Tractor scheme pigs can be kept on bare concrete or slatted floors with no comfortable bedding or suitable materials such as straw to root around in – not conditions which the RSPCA, and many shoppers, would equate with 'high welfare'."

The ASA found that Red Tractor made efforts to control the use of these methods, and that it set stringent standards for their farms with spot checks and inspections.

It also pointed out that, due to differences such as a ban on sow stalls in place in the UK since 1999, "the quality of pig welfare in the UK was high in comparison with the welfare of pigs in many European countries."

In a statement, Red Tractor said animal welfare was at the core of its standards.

"We are pleased that the ASA ruling accepts that Red Tractor pork is produced to higher standards than the EU legislation that underpins pork production in the rest of Europe, but we are slightly disappointed that the ASA felt that this obvious point of reference should have been made more explicit in the adverts.

"The fact is that much of the imported pork that we see on shelves is produced in systems that would be illegal in the UK, let alone below Red Tractor standards.

"Even changes to EU pig welfare regulations that come into effect from January 2013 still won't be on par with the Red Tractor standards."

BPEX, a division of the AHDB, said it accepted the ASA's ruling on what it considered "a small technicality".

Director Mick Sloyan said: "We will continue to promote the independently audited standards behind Red Tractor pork and pork products, including welfare, in a way that is absolutely clear to consumers."